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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Concurrency problem with _lastline in LCDSocketPoller","articleBody":"I've observed crashes like the following:\n\n```\nsep 17 11:08:19 raspberrypi java[537]: Exception in thread \"Thread-1\" java.lang.NullPointerException\nsep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Matcher.getTextLength(Matcher.java:1283)\nsep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Matcher.reset(Matcher.java:309)\nsep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Matcher.\u003cinit\u003e(Matcher.java:229)\nsep 17 11:08:19 raspberrypi java[537]: at java.util.regex.Pattern.matcher(Pattern.java:1093)\nsep 17 11:08:19 raspberrypi java[537]: at org.boncey.lcdjava.LCDSocketPoller.run(LCDSocketPoller.java:90)\nsep 17 11:08:19 raspberrypi java[537]: [main] INFO org.boncey.lcdjava.LCD - Connected\n\n```\n\nLooking inside LCDSocketPoller, it's clear that access to _lastline is not concurrency correct. A different thread (inside LCD) can call getLastLine, setting it to null, while the LCDSocketPoller thread is reading _lastline inside the run() loop. This can cause it to be equal to null on line 90, even though there is a not-null-check on line 87.\n\nUsing org.boncey.lcdjava 0.5.0\n","author":{"url":"https://github.com/antoneliasson","@type":"Person","name":"antoneliasson"},"datePublished":"2016-09-17T14:35:28.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/4/lcdjava/issues/4"}